A powder-coating installation which is provided with powder spraying devices generally has a conveyor which allows the components which are to be painted to be moved in front of spraying devices. Each component, in accordance with the size and the shape thereof, requires the flow rate of powder projected by the spraying devices to be adjusted in an appropriate manner. The spraying devices therefore need to be supplied, from a remote location, with a powder flow rate which is controlled and which can be adjusted, the powder being fluidised and conveyed by means of compressed air. The flow of powder is therefore advantageously metered, the powder is mixed with compressed air and the air/powder mixture is moved by conveying it to the powder-coating installation, in order to supply the spraying device(s) or “guns” of this installation.
An item of equipment for supplying powder to such an installation is generally produced based on the principle of a Venturi pump which has the effect of moving the powder by means of air.
Since the Venturi pump draws powder into a container which is placed under atmospheric pressure, there is consequently a limitation of the flow rate of powder in accordance with the length of the pipe between the pump and the powder-coating installation, the length of this pipe being from approximately ten to fifteen meters in accordance with the flow rate of powder desired. In any case, such a system does not allow sufficient quantities of powder to be conveyed over a large distance, in particular greater than 20 meters, and requires a high conveying speed, the minimum speed of the air in the pipe having to be in the order of from eight to ten meters per second.
Furthermore, the significant quantity of air used in this instance has a negative effect on the powder depositing yield, that is to say, on the ratio between the quantity of powder deposited and the quantity of powder sprayed. The air for conveying the powder has a tendency to blow away the powder already deposited on the component to be painted.
Furthermore, a system of this type has a tendency to cause the powder to melt owing to the friction thereof in the Venturi pump and the particles of molten powder then agglomerate and they bring about defects in the projected painting. The powder also creates an undesirable effect of abrasion in the mixing device.
As a result, other items of equipment have been proposed which allow the problems set out above to be overcome.
In particular, it is known to use an item of equipment which comprises:                a reservoir, provided for containing the powder,        means for conveying powder inside the reservoir,        means for injecting compressed air into the lower portion of the reservoir, in order to fluidise the powder, and        at least one pipe for discharging the powder carried by air, from the reservoir, this pipe being connected to at least one remote device for using the powder, in particular a spraying device.        
Such an item of equipment which is known in particular from documents EP1454675 and FR2872067, allows the flow rate of powder applied to be controlled more readily and allows the quantity of air used to be reduced, which reduces the blowing effect in particular.
Furthermore, the speed of the mixture is lower in the equipment, which prevents the powder from melting.
In known items of equipment of this type, the means for conveying the powder into the reservoir from a filling container operate by means of gravity, or by using a pump in order to move the powder, these means being associated with a valve.
These measures bring about occurrences of powder compression in the region of the valve, and therefore polymerisation and agglomeration of the powder in the region of the valve, the agglomerations of powder then bringing about defects when the powder is applied to a component to be painted.
The present invention is directed to resolving these and other matters.